Vaishnavi, a PR-cum-lobbying outfit owned by Niira Radia, started working for the Tatas in 2001. Radia handled the corporate communications of the Tata Group for several years in the last decade. For a time she had another high-profile client, Reliance Industries, India's largest private sector company. Unitech was also a client for some years starting 2005.

Radia came into the national limelight in 2010 when the so-called 'Radia Tapes' (conversations between Radia and bulge-bracket industrialists, politicians and journalists) were leaked by unknown persons.

These tapes are loosely associated with what is known as the 2G case, a sprawling investigation by various agencies into the affairs of the telecom sector between 2001 and 2008, which eventually led to high-profile arrests, including that of politicians A Raja and Kanimozhi along with industrialists - Unitech's Sanjay Chandra, DB Realty's Shahid Balwa and three top executives of the Anil Ambani group.

At its core, the 2G affair is about the controversial allotment of licences in early 2008 by former telecom minister A Raja, who is alleged to have bent the rules in the by now infamous first-come-first-served process for issuing telecom licences. Raja and a number of officials of the telecom department and some corporate executives named above are facing trial in a Delhi court.

The tapes also contain conversations between Radia and others that refer to the Unitech land deal. Radia is not an accused in the 2G case, but has appeared as a prosecution witness. As of now, there are two ongoing probes against Radia. One is the SFIO investigation described in our story. The other is a separate probe monitored by the Supreme Court after all of Radia's conversations were transcribed. The court has ordered that any violations of a criminal nature indicated in the conversations should be probed.

The allegation by CBI is that Raja helped various companies, including Unitech and Swan (an arm of real estate company DB Realty), to get hold of telecom licences even though the companies were not eligible for licences on various counts. In the case of Swan, the allegation is that it was a front company set up by the Anil Ambani group. Since the Anil Ambani group already had nation-wide telecom licences, the act of setting up Swan violated the rule, according to CBI, that a company or a group could not own more than 10% in two telecom companies in the same service area.

The investigation by CBI has subsequently embroiled two promoters of the Essar Group and two of their relatives, owners of Loop Telecom - CBI alleges that Loop is a front for Essar and violates the 10% rule. In the case of the Tatas, however, the IT department said that Unitech was a front for Tata Teleservices, but CBI did not press charges against the group as the 10% rule had not been violated.